This invention relates generally to television cathode ray tubes, and more particularly to means for supporting the getter in such tubes.
The use of the getter is old in electron tube art. The function of the getter is to absorb residual gases that remain in the envelope following the vacuum pump air evacuation process. In its most commonly used form, the getter structure comprises a small "pan" containing alloys of which the primary constituent is barium. The pan of getter is positioned close to the inner wall of the tube envelope and is heated to a high temperature, usually about 900.degree. C., by an induction coil located outside the envelope. This heating causes the getter to "flash", vaporizing the alloy and causing an effusion of the vapor in the envelope for the capture of residual gases to make a better vacuum within the envelope. The getter fallout mainly comprises a metallic residue deposited on funnel walls and on components adjacent to the area of the flash.
Problems can arise from the use of getters. One such problem is caused by the composition of the getter fall-out. The fall-out comprises a metallic residue which is electrically conductive, and can act as an electrical shunt. For example, an exposed resistive surface used for arc-suppression in the cathode ray tube can be effectively bypassed and short-circuited by deposits thereon of conductive material produced by the getter flash. Another problem from getter fall-out relates to the high voltage properties of the electron gun. If any substantial increment of metallic residue fall-out finds its way to the high electric field portion of the gun, the gun will be more susceptible to arcing and operating life may be markedly reduced.
As a result of these problems, it has been common prior art practice to locate the pan containing the getter as far away as possible from components affected by getter fall-out. In television cathode ray tubes, the pan of getter material is commonly supported by the electron gun component nearest the faceplate known as the "convergence cup," or "support cup" (as it will be termed hereafter). A structure of this type is shown by Benda in U.S. Pat. No. 3,432,712. Benda discloses a ring-like structure formed as an open trough facing the mask and containing the getter material. This ring-like structure is shown as being supported in coaxial alignment with an electron gun by a post-like positioner extending from the support cup. A similiar structure is disclosed by Johnson in U.S. Pat. No. 3,564,327.
To locate the getter and its fall-out as far as possible from the gun, it has also been common practice to attach the pan of getter to the support cup by means of a longitudinal resilient member which extends into the funnel of the cathode ray tube. As a result of its position against the slanted wall of the funnel of the tube, the effusion of the getter is projected outwardly into the funnel and generally away from the electron gun. This type of getter support structure, which is commonly known as an "antenna getter," is disclosed by Benda et al. in U.S. Pat. No. 3,961,221.